The specific aim of this research is to study the anatomical connections and organization of the basal ganglia and related nuclei in the monkey. Research will be directed toward the study of pallidofugal and nigral efferent systems using three established anatomical methods: (1) silver impregnation methods for the tracing of anterograde degeneration from discrete stereotaxic lesions, (2) serial cresyl violet stained sections for the study of retrograde cell changes resulting from axonal interruption, and (3) autoradiographic tracing of axonal connections using tritiated amino acids. Attempts will be made to: (1) define precisely the origin, course and terminations of the ansa lenticularis and lenticular fasciculus, (2) determine the projections of certain relay nuclei (ventral anterior thalamus and the pedunculopontine nuclei) which receive pallidofugal fibers, and (3) make detailed comparisons of the thalamic projections of the globus pallidus and the deep cerebellar nuclei. Attempts will be made to better define the distribution and topographical organization of nigrostriatal fiber systems which arise from the pars compacta using autoradiographic tracing technics. This method also will be used to study known nigral projections to thalamic nuclei (ventral anterior (VAmc) and ventral lateral (VLm)) and potential connections with the globus pallidus, subthalamic nucleus, midbrain tegmentum and the superior colliculus.